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S H Manglos

Publications and source records attributed to S H Manglos.

14 recordsLinked to original sources
PubMed2001

An EM algorithm for estimating SPECT emission and transmission parameters from emissions data only.

A maximum-likelihood (ML) expectation-maximization (EM) algorithm (called EM-IntraSPECT) is presented for simultaneously estimating single photon emission computed tomography (SPECT) emission and attenuation parameters from emission data alone. The algorithm uses the activity within the patient as transmission tomography sources, with which attenuation coefficients can be estimated. For this initial study, EM-IntraSPECT was tested on computer-simulated attenuation and emission maps representing a simplified human thorax as well as on SPECT data obtained from a physical phantom. Two evaluations were performed. First, to corroborate the idea of reconstructing attenuation parameters from emission data, attenuation parameters (mu) were estimated with the emission intensities (lambda) fixed at their true values. Accurate reconstructions of attenuation parameters were obtained. Second, emission parameters lambda and attenuation parameters mu were simultaneously estimated from the emission data alone. In this case there was crosstalk between estimates of lambda and mu and final estimates of lambda and mu depended on initial values. Estimates degraded significantly as the support extended out farther from the body, and an explanation for this is proposed. In the EM-IntraSPECT reconstructed attenuation images, the lungs, spine, and soft tissue were readily distinguished and had approximately correct shapes and sizes. As compared with standard EM reconstruction assuming a fix uniform attenuation map, EM-IntraSPECT provided more uniform estimates of cardiac activity in the physical phantom study and in the simulation study with tight support, but less uniform estimates with a broad support. The new EM algorithm derived here has additional applications, including reconstructing emission and transmission projection data under a unified statistical model.

Algorithms↗
PubMed1995

Transmission maximum-likelihood reconstruction with ordered subsets for cone beam CT.

An iterative algorithm is presented for accelerated reconstruction of cone beam transmission CT data (CBCT). CBCT supplies an attenuation map for SPECT attenuation compensation and anatomical correlation. Iterative algorithms are necessary to reduce truncation artifacts and 3D reconstruction artifacts. An existing transmission maximum-likelihood algorithm (TRML) is accurate but the reconstruction time is too long. The new algorithm is a modified EM algorithm, based on ordered subsets (OSEM). OSEM was evaluated in comparison to TRML using a thorax phantom and a 3D Defrise phantom. A wide range of image measures were evaluated, including spatial resolution, noise, log likelihood, region quantification, truncation artifact removal, and 3D artifact removal. For appropriate subset size, OSEM produced essentially the same image as TRML, but required only one-tenth as many iterations. Thus, adequate images were available in two to four iterations (20-30 min on a SPARC 2 workstation). Further, OSEM still approximately maximizes likelihood: divergence occurs only for very high (and clinically irrelevant) iterations. Ordered subsets are likely to be useful in other geometries (fan and parallel) and for emission CT as well. Therefore, with ordered subsets, high-quality iterative reconstruction is now available in clinically practical reconstructions times.

Algorithms↗
PubMed1993

Phantom study of breast tissue attenuation in myocardial imaging.

The attenuation of photons by the breasts and other soft tissue overlying the chest may decrease the diagnostic accuracy of SPECT myocardial imaging. In this experiment, we measured the attenuation distortion of myocardial polar maps using a thorax phantom with a cardiac insert and added breast tissue. The distortion was measured using a regional semiquantitative analysis. Attenuation compensation was performed using a conebeam radionuclide CT attenuation map. Breast tissue attenuation created apparent "defects" in the polar map, where the intensity was reduced by up to 35% relative to the most intense region. However, the size, location and severity of the reduction depended on cardiac insert orientation and breast placement. For the geometries studied, apparent "defects" were observed in the anterior wall, the apex, the inferior wall and basal regions. These results suggest that attenuation artifacts may occur in almost any location. However, the attenuation compensation nearly eliminated the apparent defects and improved polar map symmetry. After compensation, the variations between regions were generally 5% or less. Therefore, we expect that attenuation compensation will improve diagnostic accuracy in myocardial imaging in female patients and in males with excessive musculature or soft tissue. Without such compensation, diagnosis may be compromised.

Artifacts↗
PubMed1992

Persistent pain inhibits contralateral somatosensory cortical activity in humans.

To assess cortical activity during pain perception, regional cerebral blood flow (rCBF) studies were done in humans using single photon emission computed tomography (SPECT) with the radiotracer Tc99m-HMPAO and magnetic resonance imaging localization. Normalized SPECT data were analyzed by region of interest and change distribution. Contralateral somatosensory rCBF was decreased when the digits of the hand were immersed in a hot water bath for 3 min which was rated as moderately painful (persistent pain). No decrease was observed when the hand was immersed in tepid water (control). In contrast, cortical rCBF was increased during vibratory and sensorimotor tasks, in the contralateral somatosensory and sensorimotor areas, respectively. These results indicate that pain perception in man is associated with somatosensory cortical inhibition.

Adult↗
PubMed1992

Truncation artifact suppression in cone-beam radionuclide transmission CT using maximum likelihood techniques: evaluation with human subjects.

Transverse image truncation can be a serious problem for human imaging using cone-beam transmission CT (CB-CT) implemented on a conventional rotating gamma camera. If this problem can be solved, CB-CT will be useful for attenuation compensation of SPECT images. This paper presents a reconstruction method to reduce or eliminate the artifacts resulting from the truncation. The method uses a previously published transmission maximum likelihood EM algorithm, adapted to the cone-beam geometry. The reconstruction method is evaluated qualitatively using three human subjects of various dimensions and various degrees of truncation. For the two smaller subjects, with moderate truncation, the maximum likelihood method is very successful, nearly eliminating the artifacts seen with conventional filtered backprojection of truncated geometries. The use of an expanded reconstructed space, which contains the entire transverse slice of the subject, is necessary for optimal truncation removal. For the largest subject investigated, the truncation was substantial, and the artifacts were only partially removed by the maximum likelihood reconstruction. Nonetheless, the images were qualitatively superior to those obtained with filtered backprojection. An added elliptical support prior moderately increased the rate of convergence, and helped to force a reasonable body contour.

Adult↗
PubMed1992

Imaging of the human torso using cone-beam transmission CT implemented on a rotating gamma camera.

Radionuclide transmission CT generated on a rotating gamma camera can improve SPECT imaging by providing attenuation maps for attenuation compensation and for anatomical correlation. This paper demonstrates the feasibility and high quality of cone-beam transmission CT (CB-CT) of human subjects, in comparison to conventional parallel-ray CT, and evaluates some possible imaging protocols. Two CB-CT implementation modes, with a cone-beam collimator and without any collimator, were evaluated. Three human subjects of different dimensions were imaged. For the two smaller subjects, the CB-CT images were dramatically superior, in terms of noise and resolution, to those obtained with a parallel-ray geometry. The image noise was less by a factor of 6. CB-CT linear attenuation coefficients were found to be in close agreement with published values for various tissues. For the largest subject, image truncation produced a ring artifact at the edge, but inside the artifact, the image quality was still very good. Cone-beam images obtained without any collimator were acceptable, but photon scatter degraded the image contrast.

Body Height↗
PubMed1991

Cone-beam transmission computed tomography for nonuniform attenuation compensation of SPECT images.

This paper develops and tests cone-beam transmission computed tomography (CB-CT) for attenuation compensation of SPECT images. CB-CT was implemented on a rotating gamma camera with a point source (1-2 mCi) of 99mTc, and a light-weight aluminum source holder. A cone-beam collimator may be used but is not required. Since the point source is either located at the collimator focal point, or the camera is uncollimated, CB-CT has excellent sensitivity (at least 150 times that of a parallel-hole, high-resolution collimator). The predicted resolution is equal to the intrinsic gamma camera resolution (3-4 mm), which is much higher than for a high-resolution, parallel-hole collimator (10-20 mm). In the present study, CB-CT provided low noise, high-resolution attenuation maps for use in a nonuniform attenuation-weighted backprojection algorithm. The attenuation compensation accuracy was tested using basic geometries of line sources and nonuniform density models. For the appropriate scaling of the attenuation map, the attenuation compensation was accurate and removed the SPECT image distortion associated with nonuniform attenuation. Attenuation maps acquired either with cone beam collimator or without any collimator were both successful. Using CB-CT, SPECT can thus be made much more accurate without adding unduly to the imaging time, complexity, or cost.

Algorithms↗
PubMed1988

Noise characteristics for cone beam collimators: a comparison with parallel hole collimator.

In order to evaluate the properties of a cone beam (CB) collimator and three-dimensional filtered backprojection algorithm, the noise characteristics of this collimator configuration were determined and comparisons with a parallel hole (PH) collimator were made. Noise characteristics were evaluated using two approaches: the first consisted of assessing the magnitude of local random fluctuations in the reconstructed images, and the second consisted of assessing the noise texture in these images in the frequency domain by evaluating the noise power spectrum. Data used for these measurements were simulated using Monte Carlo models of SPECT systems equipped with cone beam and parallel hole collimators. Finally, to compare experimentally a specially designed high resolution CB collimator with a high resolution (HRES) PH collimator, measurements of a physical phantom were performed. Results of our studies show better noise magnitude for CB collimators; however, for CB collimators with short focal lengths (40-60 cm) the shape of %RMS noise distributions differs from slice to slice.

Computer Simulation↗
PubMed1987

Experimentally measured scatter fractions and energy spectra as a test of Monte Carlo simulations.

A method for the validation of Monte Carlo photon transport calculations is presented, with particular emphasis on the scatter component of such calculations. The method is based on a quantitative comparison of calculated and experimental scatter fractions. In addition, the method includes a qualitative comparison of point spread functions and energy spectra. An application of the method is demonstrated by comparing the results of an existing Monte Carlo code with experimental results obtained with a gamma camera viewing a point source of 99Tcm (140 keV gamma rays) centred within a water-filled cylinder. The results of the comparisons show good agreement between experiment and calculation. These results allow the code to be used with increased confidence in a variety of situations, and they define more precisely the region of applicability of the code. In addition, the determination of scatter fractions and energy spectra is useful for other applications. For example, scatter fractions can be a useful parameter for evaluating possible techniques for scatter compensation.

Computer Simulation↗
PubMed1987

Nonisotropic attenuation in SPECT: phantom tests of quantitative effects and compensation techniques.

A quantitative study of nonisotropic attenuation in SPECT imaging is presented. The study includes a case where the spatial distribution of the attenuation coefficient is nonuniform, as well as a case where the photon path length in the attenuating medium is variable as a function of direction. The effects are studied using phantoms with known source activity and density distributions. Reconstructed images of the phantoms with and without attenuation compensation are compared with the source distribution. Three methods are used to provide partial attenuation compensation, using effective attenuation coefficients. These coefficients include some of the effects of photon scatter, but scatter is not explicitly treated. One attenuation compensation method involves a multiplicative postprocessing correction using an assumed constant attenuation coefficient. A modification of this technique is implemented using the correct nonuniform attenuation map to determine the multiplication factors. A single-iteration technique is used to provide a more complete compensation. The results indicate that nonuniform attenuation can produce significant distortion in line spread functions and in larger distributed sources. This distortion can alter volume determinations, quantitation measurements, and the shape of small objects, and can cause misplacement of counts into regions of low density. The distortion cannot be eliminated by the multiplicative postprocessing correction, but the single-iteration technique can significantly decrease the distortion.

Models, Structural↗
PubMedDate not supplied

Cone beam collimation for single photon emission computed tomography: analysis, simulation, and image reconstruction using filtered backprojection.

This paper presents an analysis of two cone beam configurations (having focal lengths of 40 and 60 cm) for the acquisition of single photon emission computed tomography (SPECT) projection data. A three-dimensional filtered backprojection algorithm is used to reconstruct SPECT images of cone beam projection data obtained using Monte Carlo simulations. The mathematical analysis resulted in on-axis point source sensitivities (calculated for a distance of 15 cm from the collimator surface) for cone beam configurations that were 1.4-3 times the sensitivities of parallel-hole and fan beam geometries having similar geometric resolutions. Cone beam collimation offers the potential for improved sensitivity for SPECT devices using large-field-of-view scintillation cameras.

Humans↗
PubMedDate not supplied

Detection nonuniformity measurements and corrections for cone beam transmission CT on a gamma camera.

Cone beam transmission CT (CB-CT) improves SPECT imaging by providing high-quality attenuation maps for attenuation compensation and for correlated SPECT and CT imaging. The present work measures the detection nonuniformity for CB-CT implemented with a gamma camera, and applies nonuniformity corrections to make CB-CT more uniform and accurate. Two cone beam collimators were investigated, as well as the uncollimated cone beam geometry, using both uniformity images and CB-CT reconstructions of a uniform circular cylinder. Uniformity images were acquired as a function of point source position relative to the nominal focal point. The uniformity images for both collimators were highly nonuniform, with some regions differing by more than 15% from the average image counts per pixel, indicating that the holes do not focus to the same point. The most uniform images were obtained with the point source located at or near the nominal focal point. Radiographs estimated the misfocusing of the holes to be about 0.6 degrees in some regions. There were no indications that the hole size was nonuniform. The CB-CT reconstructions of data acquired with collimator showed no obvious signs of image artifact from the detection nonuniformities. However, low-noise simulated data with well-localized detection defects produced readily-apparent circular artifacts. The nonuniformity correction was accurate and easy to apply, and should be used whenever quantitative accuracy is required. The uniformity images acquired without collimator lacked the collimator-produced nonuniformities, but had decreased counts near the detector edge. The decrease was predictable, using simple geometric considerations. Uniform cylinder reconstructions of "without collimator" data showed a corresponding decrease in center density relative to the edge (edge-to-center ratio = 1.25), which was improved by the nonuniformity correction (ratio = 0.21). Accurate CB-CT without collimator will require further correction for photon scatter.

Gamma Cameras↗